1. Field of the Invention
This invention relates to a shield-plated corrugated tube, and particularly to a shield-plated corrugated tube which has a tube wall corrugated by repeating convex-concave portions in the axial direction of the tube to thereby be flexible, and which is designed to cover a bundle of electric wires or the like to perform mechanical protection and electromagnetic shielding of the bundle of electric wires or the like accommodated therein.
2. Background
Recently, controllers for cars, machine tools, office machines, etc. have been made with electronics, and countermeasure of these electronic equipments against electromagnetic-wave noise has become a serious problem. In the electronic equipments, wires connected thereto are apt to absorb electromagnetic-wave noise, so it is necessary to have a shield-countermeasure to shield internal conductors of the wires from external electromagnetic waves. Shielding the internal conductors is performed by grounding external conductors covering the internal conductors.
One of the external conductors used in this occasion is a shield-plated corrugated tube in which plating is applied on a flexible and bellows like tube (corrugated tube) made from resin material. The shield-plated corrugated tube is obtained by plating a corrugated tube, originally used as a wiring protector, in order to make the corrugated tube also have a shielding effect. In the shield-plated corrugated tube, a slit for insertion of wires is formed in the axial direction (longitudinal direction) of the tube in the same manner as in a conventional corrugated tube.
FIG. 7 shows a structural example of such a conventional shield corrugated tube.
In this shield corrugated tube 1, an electromagnetically shielding metal layer 5 is provided on the inner surface of a corrugated tube 3 formed from insulating resin material and having flexibility.
As illustrated, the corrugated tube 3 has a structure in which a tube wall is formed into a corrugated (bellows-like) shape so as to repeat predetermined convex-concave portions in the axial direction of the tube, and which has a slit 7 parting the tube wall in the axial direction of the tube. If the slit 7 is opened and the corrugated tube 7 is made to cover a bundle of electric wires or the like, the bundle of electric wires or the like can be accommodated therein easily, and mechanical protection and electromagnetic shielding of the accommodated bundle of electric wires or the like can be attained.
Examples of the method of providing such a metal layer include a method in which a corrugated pipe formed of metal is used as the metal layer, and the surface of the metal pipe is coated with an insulating resin layer; a method in which metal such as aluminum is evaporated onto a corrugated tube which has been made from insulating resin in advance; a method in which an electrically conductive paint is applied onto on a corrugated tube which has been made from insulating resin in advance; and so on.
However, in the above mentioned method using a metal pipe, it is difficult to form a coating of an insulating resin layer, so that there arise a problem that the cost is increased, and a problem that the flexibility is poor.
In the method by using evaporation, since it is impossible to make the metal layer thick, it is difficult to make the performance of shielding high. In addition, since there occurs a difference in the thickness of the metal layer between the vertical surface and the horizontal surface in the convex-concave portions, there arises a problem with the unstable shielding performance.
In the method in which electrically conductive coating is applied in the form of paint, it is difficult to perform uniform application of paint, so that there is a problem of unstable shielding performance further this method is not suitable for manufacturing a long shielded corrugated tube.
Electromagnetic shielding is attained by the electromagnetic wave reflection and absorption functions of a metal layer. However, in each of the above-mentioned methods, a thin metal layer can be formed on only either one of the inner and outer surfaces of a corrugated tube, and particularly the effect of reflection can be obtained only once by one sheet of the thin metal layer. Accordingly, there is a basic problem that it is difficult to obtain a sufficient electromagnetically shielding effect.
Under such a background, it has been therefore considered that such metal layers are formed on both the inner and outer surfaces of a corrugated tube made from insulating resin by employing the method of electroless plating. However, in the case where the electroless plating method is employed, bubbles generated during a plating process are collected in concave portions in the corrugated tube, or a plating solution remains, so that it is easy to produce a failure in plating.
Therefore, it is regarded as a problem to be solved in the future to prevent bubbles from being collected in concave portions in the corrugated tube during a plating process, to prevent a plating solution from remaining, and so on.